Actuator, optical scanner and image-forming device

ABSTRACT

An actuator, includes: a weight part; a supporting part supporting the weight part; a connecting part coupling the weight part rotatable to the supporting part and having an elastic part; a driving member for driving and rotating the weight part; and a semiconductor circuit for driving the weight part. The driving member is operated to torsionally deform the elastic part and rotate the weight part. The elastic part has a first silicon part that is mainly made of silicon and a first resin part that is mainly made of resin and coupled to the first silicon part. The supporting part has at least a second silicon part made mainly of silicon and coupled to the first silicon part of the elastic part. The semiconductor circuit is provided on the second silicon part of the supporting part.

CROSS-REFERENCE TO A RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.12/767,914 filed Apr. 27, 2010 which was a continuation of U.S. patentapplication Ser. No. 11/856,135 filed Sep. 17, 2007 which claimedpriority to Japanese Patent Application Number 2006-255085 filed Sep.20, 2006. The entire disclosures of these applications are expresslyincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to an actuator, an optical scanner and animage-forming device.

2. Related Art

JP-A-2004-191953 is a first example of related art, and JP-A-2005-326463is a second example of the related art.

As an example of an optical scanner which is for drawing an imagethrough optical-beam scanning and equipped in a laser printer or thelike, one using an actuator having a torsional vibrating element hasbeen known (see the first example.)

The first example discloses an actuator having a torsional vibratingelement of a single-degree-of-freedom vibration system. This actuatorhas the torsional vibrating element of a single-degree-of-freedomvibration system that includes a weight member, a fixing frame and apair of torsional springs that couples the weight member rotatable tothe fixing frame. The both sides of the weight member are supported bythe torsional springs. A light reflecting part that has a lightreflectivity is provided on the weight member. The weight member turnswhen the pair of the torsional springs is distorted and deformed. Lightis reflected at the light reflecting part and the scanning is performed.In this way, an image can be drawn through the optical-beam scanning.

In this actuator, the weight member, the pair of the torsional springsand the fixing frame are fabricated together so as to form a single bodyby etching a silicone substrate (a silicon wafer).

When the weight member should be turned rapidly, a torsional springconstant of the elastic part has to be high. There are two ways, forexample, to make the torsional spring constant high: one is to make thethickness of the elastic part larger, and the other is to make thelongitudinal length of the elastic part shorter.

However, when the above-two ways are applied to silicon which isrelatively hard material, the amount of a change in the torsional springconstant with respect to a change in the length or/and the thickness ofthe elastic part becomes too large. In other words, it is difficult toperform a fine adjustment of the torsional spring constant at theelastic part.

When the weight member should be turned slowly, the torsional springconstant of the elastic part has to be low. There are two ways, forexample, to make the torsional spring constant high: one is to make thelongitudinal length of the torsional spring longer, and the other is toincrease the weight of the weight member.

However, the above-two ways increases the size of the actuator. Thismeans that it is difficult to drive the weight member slowly whiledownsizing the actuator at the same time. For these reason, the actuatoraccording to the first example has difficulty in downsizing and the fineadjustment of the torsional spring constant. Therefore, the actuatoraccording to the first example cannot be accommodated for manyapplications (for example a high-speed driving actuator, a low-speeddriving actuator and the like).

The second example discloses an optical deflector having a torsionalvibrating element of a single-degree-of-freedom vibration system. Theoptical deflector has the torsional vibrating element of thesingle-degree-of-freedom vibration system which includes a movable plateof which two sides are held by elastic support members (torsionalsprings). A reflective face (a micro-mirror) having a light reflectivityis provided on the movable plate. The movable plate turns when theelastic support members are distorted and deformed. Light is reflectedat the reflective face and the scanning is performed. In this way, aimage can be drawn through the optical-beam scanning.

In the optical deflector, a strain gauge whose resistance changescorresponding to the degree of the distortion of the elastic supportmember is provided. A torsional strain detection circuit detects thevariation in the resistance of the strain gauge and a driving circuit ofthe optical deflector is controlled based on the results obtainedthrough the detection circuit. Thereby a highly accurate scanning can beperformed.

However, according to the second example, the torsional strain detectioncircuit or/and the driving circuit are not provided in the opticaldeflector itself. Therefore, the size of the deflector will become largeif these are installed in the deflector and it is difficult to downsizethe deflector.

SUMMARY

An advantage of the present invention is to provide an actuator withwhich a fine adjustment of a spring constant is possible whiledownsizing, and to provide an optical scanner and an image formingdevice thereof.

An actuator according to a first aspect of the invention includes aweight part, a supporting part supporting the weight part, a connectingpart coupling the weight part rotatable to the supporting part andhaving an elastic part, a driving member for driving and rotating theweight part, a semiconductor circuit for driving the weight part,wherein the driving member is operated to torsionally deform the elasticpart and rotate the weight part, the elastic part has a first siliconpart that is mainly made of silicon and a first resin part that ismainly made of resin and coupled to the first silicon part, thesupporting part has at least a second silicon part made mainly ofsilicon and coupled to the first silicon part of the elastic part, andthe semiconductor circuit is provided on the second silicon part of thesupporting part. According to the first aspect of the invention, it ispossible to provide the actuator in which a fine adjustment of a springconstant is possible while reducing the size of the actuator.

It is preferable that the actuator further include a behavior detectordetecting a behavior of the weight part, the behavior detector includinga stress detection element provided on the elastic part, and anamplifier circuit coupled to the stress detection element, the behaviordetector detecting the behavior of the weight part based on a signalfrom the amplifier circuit, wherein the semiconductor circuit includesthe amplifier circuit. In this way, the distance between the amplifiercircuit and the stress detection element can be made small. Thisprevents noise from being generated between the amplifier circuit andthe stress detection element thereby the behavior of the weight membercan be more precisely detected.

Alternatively it is preferable that the actuator further include abehavior detector detecting a behavior of the weight part, the behaviordetector including a light receiving element provided on the weightpart, and an amplifier circuit coupled to the light receiving element,the behavior detector detecting the behavior of the weight part based ona signal from the amplifier circuit, wherein the semiconductor circuitincludes the amplifier circuit. In this way, the distance between theamplifier circuit and the light receiving element can be made small.This prevents noise from being generated between the amplifier circuitand the light receiving element thereby the behavior of the weightmember can be more precisely detected.

It is also preferable that the actuator further include a controllercontrolling the operation of the driving member based on a detectionresult of the behavior detector. In this way, the actuator can berotated with a desired rotation characteristic.

It is also preferable that the first silicon part of the elastic partand the first resin part of the elastic part be layered in a thicknessdirection of the weight part when the weight part is viewed in plan. Inthis way, the elastic part can be formed so as to be symmetric withrespect to the parallel line and the perpendicular line to therotational central axis of the weight part when it is viewed in plan.Thereby the weight part can be stably rotated.

It is also preferable that the elastic part have an elongate rectangularshape and the first silicon part is formed throughout the elastic partin a longitudinal direction of the elastic part. In this way, themechanical strength of the actuator can be improved.

It is also preferable that the first resin part be formed throughout theelastic part in the longitudinal direction of the elastic part. In thisway, it is possible to prevent the variation in the torsional springconstants of a pair of the elastic part caused by the positionaldisplacement between the first silicon part of the elastic part and thefirst resin part of the elastic part.

It is also preferable that a thickness of the elastic part be uniformthroughout the elastic part in the longitudinal direction. In this waythe physical characteristic of the elastic part can be made uniformthroughout the elastic part in the longitudinal direction.

It is also preferable that a thickness of the first silicon part of theelastic part be uniform throughout the elastic part in the longitudinaldirection. In this way the physical characteristic of the elastic partcan be made uniform throughout the elastic part in the longitudinaldirection.

It is preferable that the supporting part have the second resin partthat is formed so as to have a single body integrally with the firstresin part of the elastic part and is made of the same material as thematerial forming the first resin part. In this way, it is possible toenhance the mechanical strength of the actuator.

It is preferable that the second resin part of the supporting part beformed so as to cover the semiconductor circuit. With this structure, awiring for the amplifier circuit and the like can be formed on thesecond resin part of the supporting part. This can prevent short-circuitin the semiconductor circuit. Moreover, this expands the design freedomof the wiring pattern and the like and it is possible to simplify themanufacturing process of the actuator.

It is preferable that the weight part have a third resin part that isformed so as to have a single body integrally with the first resin partof the elastic part and is made of the same material as the materialforming the first resin part. In this way, it is possible to enhance themechanical strength of the actuator.

It is preferable that the driving member include a coil provided on thethird resin part of the weight part and a voltage supply applying avoltage to the coil, the weight part is rotated by applying the voltageto the coil through the voltage supply. In this way, the third resinpart of the weight part serves as an insulating layer and this canprevent short-circuit between the coils. In addition, it is notnecessary to separately provide an insulating layer so that themanufacturing process of the actuator can be simplified.

It is preferable that a light reflecting part having a light reflectingproperty be provided on the weight part. In this way, the actuator canbe used as an optical device.

An optical scanner according to a second aspect of the inventionincludes a weight part having a light reflecting part that has a lightreflecting property; a supporting part supporting the weight part; aconnecting part coupling the weight part rotatable to the supportingpart and having an elastic part; a driving member for driving androtating the weight part; and a semiconductor circuit for driving theweight part, wherein the driving member is operated to torsionallydeform the elastic part and rotate the weight part, the elastic part hasa first silicon part that is mainly made of silicon and a first resinpart that is mainly made of resin and coupled to the first silicon part,the supporting part has at least a second silicon part made mainly ofsilicon and coupled to the first silicon part of the elastic part, thesemiconductor circuit is provided on the second silicon part of thesupporting part, and the scanner scans a light beam reflected by thelight reflecting part. According to the second aspect of the invention,it is possible to provide the optical scanner in which a fine adjustmentof a spring constant is possible while reducing the size of the opticalscanner.

An image-forming device according to a third aspect of the inventionincludes an optical scanner which includes a weight part having a lightreflecting part that has a light reflecting property; a supporting partsupporting the weight part; a connecting part coupling the weight partrotatable to the supporting part and having an elastic part; a drivingmember for driving and rotating the weight part; and a semiconductorcircuit for driving the weight part, wherein the driving member isoperated to torsionally deform the elastic part and rotate the weightpart, the elastic part has a first silicon part that is mainly made ofsilicon and a first resin part that is mainly made of resin and coupledto the first silicon part, the supporting part has at least a secondsilicon part made mainly of silicon and coupled to the first siliconpart of the elastic part, the semiconductor circuit is provided on thesecond silicon part of the supporting part, and the scanner scans alight beam reflected by the light reflecting part. According to thethird aspect of the invention, it is possible to offer the small sizedimage-forming device which has a fine image drawing characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a perspective view of an actuator according to a firstembodiment of the invention.

FIG. 2 is a sectional view along the line A-A in FIG. 1.

FIG. 3 is an explanatory drawing for a driving member.

FIG. 4 is a sectional view along the line B-B in FIG. 1.

FIG. 5 is an explanatory drawing for a behavior detector and asemiconductor circuit.

FIG. 6 is a block diagram for explaining a control system.

FIGS. 7A-7F are drawings for describing a method of manufacturing anactuator according to the invention.

FIGS. 8A-8D are drawings for describing a method of manufacturing anactuator according to the invention

FIG. 9 is a perspective view of the actuator according to the firstembodiment.

FIG. 10 is an explanatory drawing for a behavior detector and asemiconductor circuit.

FIG. 11 is a schematic drawing for describing an image forming deviceaccording to the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the invention for an actuator, an optical scanner and animage-forming device will be described.

First Embodiment

An actuator according to a first embodiment of the invention is nowdescribed.

FIG. 1 is a perspective view of the actuator according to the firstembodiment, FIG. 2 is a sectional view along the line A-A in FIG. 1,FIG. 3 is an explanatory drawing for a driving member and asemiconductor circuit, FIG. 4 is a sectional view along the line B-B inFIG. 1, FIG. 5 is an explanatory drawing for a semiconductor circuit,and FIG. 6 is a block diagram for explaining a control system.

In the following description, near, far, right, and left in the pages ofFIG. 1 and FIG. 3 will be referred to as “upper,” “lower,” “right,” and“left,” respectively. Upper, lower, right and left in the pages of FIG.2 and FIG. 4 will be referred to as “upper”, “lower”, “right” and “left”respectively.

Referring to FIG. 1, an actuator 1 includes a base member 2 having asingle-degree-of-freedom vibration system and a supporting substrate 3that supports the base member 2. The actuator 1 further includes adriving member 4 which turns a weight part 21, a behavior detector 5which detects behaviors of the weight part 21 and a controller 6 thatcontrols the driving of the driving member 4.

The base member 2 includes the weight part 21, a pair of connectingparts 22, 23, and a pair of supporting parts 24, 25. The connectingparts 22, 23 are formed from elastic parts which are flexible anddeformable and have an elongate rectangular shape thereby the connectingparts 22, 23 can be also referred as elastic parts 22, 23 respectivelyin the following description.

The pair of the elastic parts 22, 23 are distorted and deformed when avoltage is applied to a hereunder-described coil 43, this turns roundthe weight part 21 in the actuator 1. The weight part 21 is rotated onthe X-rotational central axis which is shown in FIG. 1. The pair of theelastic parts 22, 23 is provided so as to be substantially symmetricwith respect to the weight part 21 as the center when the weight part 21is not driven and viewed in plan. In other words, the actuator 1 isformed so as to produce a symmetric appearance with respect to theweight part 21 as the center when the weight part 21 is not driven andviewed in plan.

The weight part 21 includes a silicon part 211 that is made mainly fromsilicon and has a plate shape, a resin part 212 whose face is adhered toa lower face (a face opposing the supporting substrate 3) of the siliconpart 211, and a light reflecting part 213 that is provided on a upperface (an opposite face to the resin part 212) of the silicon part 211.In other words the weight part 21 has a layered structure in which theresin part 212 is formed on one side of the silicon part 211 and thelight reflecting part 213 is formed on the other side of the siliconpart 211 and these layers are stuck in the thickness direction of theplane of the silicon part 211. The resin part 212 and the lightreflecting part 213 sandwiches the silicon part 211 therebetween andthis three-layered structure forms the weight part 21.

A hardness of the silicon forming the silicon part 211 of the weightpart 21 is usually harder (less warped) than the resin material formingthe resin part 212 of the weight part 21. Therefore it is possible toenhance the mechanical strength of the weight part 21 and warpage,distortion and deflection of the weight part 21 can be controlled.

The hereunder-described coil 43 is provided on a lower face (a faceopposite to the silicon part 211) of the resin part 212 in the weightpart 21.

The supporting part 24 includes a silicon part 241 that is made mainlyfrom silicon and has a plate shape, and a resin part 242 whoseplate-shaped face is adhered to a lower face of the silicon part 241 andwhich is made mainly from resin. The resin part 242 is layered over thesilicon part 241. In the same manner, the supporting part 25 includes asilicon part 251 that is made mainly from silicon and has a plate shape,and a resin part 252 whose plate-shaped face is adhered to a lower faceof the silicon part 251 and the a resin part 252 is made mainly fromresin. A hereinafter-described amplifier circuit (a semiconductorcircuit) 52 is formed on a lower face of the silicon part 241 of thesupporting part 24.

The elastic part 22 couples the weight part 21 to the supporting part 24so as to make the weight part 21 rotatable with respect to thesupporting part 24. In the same manner, the elastic part 23 couples theweight part 21 to the supporting part 25 so as to make the weight part21 rotatable with respect to the supporting part 25. The elastic parts22, 23 are formed to have the same shape and size.

The elastic part 22 and the elastic part 23 are situated on the sameaxis. The weight part 21 rotates on the axis of these elastic partswhich is the X-rotational central axis (axis of the rotation) againstthe supporting parts 24, 25. A hereinafter-described stress detectionelement 51 is provided in the elastic part 22.

The elastic part 22 and the elastic part 23 are now described in detail.The elastic part 22 and the elastic part 23 have the same structure sothat only the elastic part 22 will be described as the typical exampleand description of the elastic part 23 will be hereunder omitted.

The elastic part 22 has a silicon part 221 that is mainly made fromsilicon, and a resin part 222 that is mainly made from resin and coupledto the silicon part 221. With this structure, it is possible to performa fine adjustment of the torsional spring constant of the elastic part22. More specifically describing this, a hardness of resin material isgenerally lower (in other words softer) than that of silicon. Forexample, where the torsional spring constant of the elastic part 22 isvaried by changing the thickness (the length in the perpendiculardirection to the face of the weight part 21) of the elastic part 22, theamount of the variation in the torsional spring constant of the elasticpart 22 relative to the amount of the change in the thickness of theresin part 222 is smaller than the amount of the variation in thetorsional spring constant of the elastic part 22 relative to the amountof the change in the thickness of the silicon part 221. It follows thatthe fine adjustment of the torsional spring constant of the elastic part22 is possible by changing the thickness (film thickness) of the resinpart 222.

The torsional spring constant of the elastic part 22 can be changed in awide range by adjusting (changing) a structural proportion (such as thethickness ratio) of the resin part 222 to the silicon part 221.Moreover, the amplifier circuit (the semiconductor circuit) 52 is formedin the supporting part 24 as described above so that the supporting part24 can be utilized. In this way it is possible to provide the actuator 1which can be easily changed according to an application (for example ahigh-speed driving actuator, a low-speed driving actuator and the like)while the size of the actuator 1 is minimized. Furthermore, the actuator1 can be modified to various applications by simply changing thethickness of the elastic parts 22, 23 without changing the planar shapeof the actuator 1. Therefore it is possible to simplify themanufacturing method of the actuator 1 and reduce the manufacturingcost.

The silicon part 221 of the elastic part 22 and the resin part 222 ofthe elastic part 22 are layered in the thickness direction of the weightpart 21 (the perpendicular direction to the face of the weight part 21)when these parts are viewed in plan. Thereby it is possible to adjust(change or perform a fine adjustment of) torsional spring constant ofthe elastic part 22 by changing the thickness of the silicon part 221and/or the thickness of the resin part 222 (the length in theperpendicular direction to the face of the weight part 21). Furthermorethe elastic part 22 is formed so as to be symmetric with respect to theparallel line and the perpendicular line to the X-rotational centralaxis when it is viewed in plan. Thereby the weight part 21 can besymmetrically rotated on the X-rotational central axis.

The silicon part 221 in the elastic part 22 is formed throughout thearea of the elastic part 22 in the longitudinal direction. This canenhances the mechanical strength of the actuator 1. The resin part 222in the elastic part 22 is also formed throughout the area of the elasticpart 22 in the longitudinal direction. The spring constant of theelastic part 22 can fluctuate if the position of the silicon part 221 isdisplaced from the position of the resin part 222. This can be preventedaccording to the embodiment and the actuator 1 can exert the desiredvibration characteristics.

The elastic part 22 is formed so as to have a uniform thicknessthroughout the elastic part 22 in the longitudinal direction. Thesilicon part 221 is also formed to have a uniform thickness throughoutthe elastic part 22 in the longitudinal direction. The resin part 222 isfurther formed to have a uniform thickness throughout the elastic part22 in the longitudinal direction. Thereby physical characteristic of theelastic part 22 can be made uniform in the longitudinal direction.Consequently, it is possible to rotate the weight part 21 stably.

Relation between the thickness of the silicon part 221 and the thicknessof the resin part 222 is now described. For the sake of simplicity,assume that the planar shape of the elastic part 22 remain unchanged. Inother words, assume that the length and width of the elastic part 22don't change.

As described above, the hardness of the resin material forming the resinpart 222 is generally lower (in other words softer) than the hardness ofsilicon. Accordingly if the thickness of the elastic part 22 isconstant, the smaller the thickness of the silicon part 221 becomes, thesmaller the torsional spring constant of the elastic part 22 becomes. Onthe contrary, the larger the thickness of the silicon part 221 becomes,the larger the torsional spring constant of the elastic part 22 becomes.In other words, when the thickness of the elastic part 22 is constant,the smaller the thickness of the resin part 222 becomes, the larger thetorsional spring constant of the elastic part 22 becomes. On thecontrary, the larger the thickness of the resin part 222 becomes, thesmaller the torsional spring constant of the elastic part 22 becomes.

By adjusting the thickness of the silicon part 221 and the thickness ofthe resin part 222 in the above-described manner, it is possible toroughly adjust the torsional spring constant of the elastic part 22. Afine adjustment of the torsional spring constant of the elastic part 22can be further performed by changing the thickness of the resin part222.

In this way, the torsional spring constant of the elastic part 22 can bechanged both in a wide range and a very small range according to theembodiment of the actuator 1.

Though the elastic part 22 has been described above, the elastic part 22also has the same structure including the silicon part 221 and the resinpart 223 (the description is omitted here as mentioned above). Accordingto the embodiment of the actuator 1, it is possible to adjust (change)the torsional spring constants of the elastic parts 22, 23 both in awide rage and a very small range.

The weight part 21, the elastic parts 22, 23, and the supporting parts24, 25 have been described. The weight member 21, t the elastic parts22, 23, and the supporting parts 24, 25 are fabricated (integrated) soas to form a single body.

The base member 2 has a layered structure of the silicon layers and theresin layers. The silicon layer includes the silicon part 211 of theweight member 21, the silicon part 221 of the elastic part 22, thesilicon part 231 of the elastic part 23, the silicon part 241 of thesupporting part 24 and the silicon part 251 of the supporting part 25,and these are fabricated so as to form a single body. While the resinlayer includes the resin part 212 of the weight part 21, the resin part222 of the elastic part 22, the resin part 232 of the elastic part 23,the resin part 242 of the supporting part 24 and the resin part 252 ofthe supporting part 25, and these are fabricated so as to form a singlebody.

Such base member 2 can be obtained by for example forming the resinlayer on a silicon wafer and etching the layer so as to have thecorresponding planar shapes of the weight part 21, the elastic parts 22,23, and the supporting parts 24, 25. In this way, it is possible tosimplify the manufacturing process of the base member 2.

Places where the stress most concentrates in the base member 2 when theweight member 21 rotates are the boundaries between the weight part 21and the elastic parts 22, 23, the boundary between the elastic part 22and the supporting part 24, and the boundary between the elastic part 23and the supporting part 25. According to the embodiment, the weightmember 21, the elastic parts 22, 23, and the supporting parts 24, 25 arefabricated so as to form the single body so that it is possible toimprove the mechanical strength compared to the case where the weightmember 21, the elastic parts 22, 23, and the supporting parts 24, 25 arefabricated separately (for example the junction of the weight member 21and the elastic part 22 is situated at the boundary between the weightmember 21 and the elastic part 22). Consequently, the endurance of theactuator 1 can be improved and such actuator 1 will be operated stablyfor a long time period.

The resin part 212 of the weight part 21, the resin part 222 of theelastic part 22, the resin part 232 of the elastic part 23, the resinpart 242 of the supporting part 24 and the resin part 252 of thesupporting part 25 are made from the same resin material and so as toform a single body. Any resin materials can be used for the resin layersprovided that the weight member 21 is rotatable. For instance variousthermoplastic resins and various thermo-setting resins can be used.However it is preferable that thermo-setting resin be used since it hasa fine heat resistance and it cannot be easily deteriorated or altered.Therefore the actuator 1 can maintain (exert) a desired rotationproperty for a long time period by adopting the thermo-setting resin.Such thermo-setting resin is not particularly limited, for example apolyimide resin, a phenol resin, an epoxy resin, an unsaturatedpolyester resin, a urea resin, a melamine resin, a diallyl phthalateresin or the like can be appropriately used.

Where the actuator 1 is applied to an optical device such as an opticalscanner, the temperature of the weight member 21 can rise with the lightwhich is not reflected by the light reflecting part 213. Therefore it ispreferable that the resin material having a relatively high meltingpoint or softening point be used though it depends on the conditions inwhich the actuator is used. In this way, it is possible to prevent thespring constant from being radically (significantly) changed with therising temperature at the elastic parts 22, 23. Accordingly, theactuator 1 can maintain (exert) a desired scan performance even if theactuator is continuously used for a long time period.

The base member 2 is supported by the supporting substrate 3. A pair ofconvex portions 32, 33 is formed on the upper face (the face opposingthe base member 2) of the supporting substrate 3 and in the positionwhere faces the supporting part 24. In other words, a concave portion 30is formed on the upper face of the supporting substrate 3. Thesupporting substrate 3 holds the base member 2 through the supportingparts 24, 25 whose upper faces are coupled to the upper faces of theconvex portions 32, 33 respectively.

An opening 31 is provided in the bottom face of the concave portion 30and at the position where corresponds to the weight member 21. Thisopening 31 serves as a clearance groove which prevents the weight member21 from contacting the supporting substrate 3 when the weight member 21rotates (vibrates). By providing such opening 31 (clearance portion), itis possible to set a larger sway angle (vibration amplitude) of theweight member 21 while keeping the size of the actuator 1 small.

The above-mentioned clearance portion is not necessarily the openingsituated at the lower face (the opposite face to the base member 2) ofthe supporting substrate 3 provided it can sufficiently exert theabove-described function as a clearance. For example the clearanceportion can be a concave portion formed in the upper face of thesupporting substrate 3. In case where the depth of the concave portion30 (the height of the convex portions 32, 33) is larger than the swayangle (vibration amplitude) of the weight member 21, it is not necessaryto provide the opening 31. The supporting substrate 3 may not benecessary depending on the shape of the supporting parts 24, 25 of thebase member 2. The supporting substrate 3 is made of for example mainlyglass, silicon or the like.

The driving member 4 that is for turning round the weight member 21 willbe now described with reference to FIG. 3. FIG. 3 is a partial sectionalenlarged view of the lower face (the face opposing the supportingsubstrate 3) of the base member 2.

Referring to FIG. 3, the driving member 4 includes the coil 43 providedin the resin part 212 of the weight member 21, a AC power source (avoltage supply) 44 that applies voltage to the coil 43, and a pair ofmagnets provided such that they oppose each other in the directionperpendicular to the X-rotational central axis and they sandwich theweight member 21. Such driving member 4 vibrates (rotates) the weightmember 21 with respect to the supporting parts 24, 25 by applying an ACvoltage to the coil 43 from the AC power source 44.

The coil 43 is formed throughout the lower face (the opposite face tothe supporting substrate 3) of the resin part 212 of the weight member21 in a volute shape. The resin part 212 serves as an insulating layerso that short-circuit among wirings of the coil 43 can be prevented. Ina case where the coil 43 is provided on the silicon part 211, forexample, an insulating layer (oxide film layer) has to be separatelyprovided on the resin part 212. According to the actuator 1 of theembodiment, such process to provided an insulating layer is notnecessary (can be omitted). The manufacturing process of the actuator 1can be simplified in this sense. The patterning figure of the coil 43 isnot particularly limited as long as the weight member 21 is maderotatable with it.

One end of the wiring (electric wiring) consisting the coil 43 iscoupled to a terminal 431 provided on the supporting part 24, and theother end of the wiring is coupled to a terminal 432 provided on thesupporting part 25. The terminals 431, 423 are coupled to the AC powersource 44. A magnetic field is generated from the coil 43 when an ACvoltage is applied to the coil 43 from the AC power source 44.

A magnet 41 and a magnet 42 are provided such that they oppose eachother in the direction perpendicular to the X-rotational central axisand they sandwich the weight member 21. The face of the magnet 41opposing the magnet 42 has the opposite magnetic polarity to thepolarity of the face of the magnet 42 opposing the magnet 41. Anymagnets can be adopted as such magnets 41, 42. For example, permanentmagnets (hard magnetic substances) such as a neodymium magnet, a ferritemagnet, a samarium-cobalt magnet and an alnico magnet can beappropriately used.

The driving member 4 vibrates (rotates) the weight member 21 in thefollowing way. For an illustrative purpose, assume that the face of themagnet 41 opposing the magnet 42 is the south pole and the face of themagnet 42 opposing the magnet 42 is the north pole as shown in FIG. 4.For the sake of description, “upper” and “lower” in the page of FIG. 4is called “upper” and “lower” in the following description.

The case (hereinafter called a “first state”) where a current suppliedby the AC power source 44 flows from the terminal 431 to the terminal432 through the coil 43 is described. In this case, a downwardelectromagnetic force works at a part of the weight member 21 which isthe magnet 42 side with respect to the X-rotational central axis, thedownward is the lower side in FIG. 4 (Fleming's left-hand rule is hereapplied). On the contrary, an upward electromagnetic force works at theother part of the weight member 21 which is the magnet 41 side withrespect to the X-rotational central axis, the upward is the upper sidein FIG. 4. Thereby the weight member 21 rotates counterclockwise on theX-rotational central axis in FIG. 4.

On the contrary, in the case (hereinafter called a “second state”) wherea current supplied by the AC power source 44 flows from the terminal 432to the terminal 431 through the coil 43, the upward electromagneticforce works at the part of the weight member 21 which is the magnet 42side with respect to the X-rotational central axis, the upward is theupper side in FIG. 4. The downward electromagnetic force works at theother part of the weight member 21 which is the magnet 41 side withrespect to the X-rotational central axis, the downward is the lower sidein FIG. 4. Thereby the weight member 21 rotates clockwise on theX-rotational central axis in FIG. 4.

The elastic parts 22, 23 are twisted and deformed when theabove-mentioned first state and the second state are alternativelyrepeated. In this way, the weight member 21 is rotated with respect tothe supporting part 24.

By using the AC power source 44 as the voltage supply means, the firststate and the second state can be switched periodically and smoothly sothat the weight member 21 is rotated smoothly. The voltage supply is notparticularly limited as long as it can apply voltage to the coil 43though the embodiment used the AC power source 44. A DC power source canbe for example used instead. In this case, the weight member 21 can berotated with respect to the supporting part 24 by applying a DC voltageintermittently to the coil 43.

The behavior detector 5 which detects behaviors of the weight part 21 isnow described.

Referring to FIG. 3 and FIG. 5, the behavior detector 5 includes thestress detection element 51 provided on the lower face (the face in theresin part 222 side) of the silicon part 222 in the elastic part 22, andthe amplifier circuit 52 (the semiconductor circuit) that is provided onthe silicon part 241 of the supporting part 24 and is electricallycoupled to the stress detection element 51. A plurality of through holes53 through which the stress detection element 51 and the amplifiercircuit 52 are coupled each other. An input terminal 521 and an outputterminal 522 are provided on the resin part 242 of the supporting part24. These terminals are electrically coupled to the amplifier circuit52.

The behavior detector 5 is configured so as to detect the behavior ofthe weight member 21 based on a signal from the amplifier circuit 52.More specifically, the stress detection element 51 has a property thatthe resistance value changes according to the degree of the deformation.By providing such stress detection element 51 on the elastic part 22, itis possible to vary the resistance of the stress detection element 51according to the amount of the torsional deformation of the elastic part22 (in other words according to the rotation angle of the weight member21).

A value of the current (the electric signal) that flows through thestress detection element 51 changes when the resistance value of thestress detection element 51 varies, that variation in the electricsignal is amplified by the amplifier circuit 52. The behavior of theweight member 21 is detected based on the amplified signal. In this way,the behavior of the weight member 21 can be precisely detected. Thevariation in the value of the current (the electric signal) caused bythe variation in the resistance value of the stress detection element 51is so small that the electric signal is amplified through the amplifiercircuit 52 in this embodiment in order to precisely detect the behaviorof the weight member 21.

The amplifier circuit 52 is formed on the silicon part 241 of thesupporting part 24 so that the supporting part 24 can be efficientlyused. In this way, it is possible to minimize the actuator 1. Suchamplifier circuit 52 can be formed by for example diffusing an impuritysuch as boron, iridium, potassium or the like around the surface of thesilicon part 241.

According to the embodiment, the amplifier circuit 52 is placed close tothe stress detection element 51 and the distance between the amplifiercircuit 52 and the stress detection element 51 is very small. Therebythe length of the wiring that couples the amplifier circuit 52 and thestress detection element 51 can be made short. This prevents noise frombeing generated between the amplifier circuit 52 and the stressdetection element 51 thereby the behavior of the weight member 21 can bemore precisely detected.

Here, the distance between the stress detection element 51 and theamplifier circuit 52 can be made shorter by for example providing theamplifier circuit 52 on the silicon part 211 of the weight member 21. Inother words, the same advantageous effect as the embodiment of theactuator 1 can be obtained when the amplifier circuit 52 is formed onthe silicon part 211 of the weight member 21. However, a mass of theweight member 21 can be made smaller when the amplifier circuit 52 isformed on the supporting part 24 compared with when the amplifiercircuit 52 is formed on the weight member 21. This means that theactuator 1 can be easily accommodated both to high-speed driving and tolow-speed driving when the amplifier circuit 52 is formed on thesupporting part 24. Meanwhile where the actuator 1 is applied to anoptical device such as an optical scanner, the temperature of the weightmember 21 can rise with the light which is not reflected by the lightreflecting part 213. The amplifier circuit 52 will be less affected byheat when the amplifier circuit 52 is formed on the supporting part 24like this embodiment compared with when the amplifier circuit 52 isprovided on the weight member 21. Consequently, it is possible to detectthe behavior of the weight member 21 more precisely.

On the lower face of the silicon part 241 where the amplifier circuit 52is provided, the resin part 242 is further provided so as to cover theamplifier circuit 52. With this structure, a wiring for the amplifiercircuit 52 can be patterned on a lower face of the resin part 242. Thisexpands the design freedom and it is possible to simplify themanufacturing process of the actuator 1.

The actuator 1 has the controller 6 that controls the operation of thedriving member 4 based on the detection results of the above-describedbehavior detector 5. Referring to FIG. 6, the controller 6 controls theAC power source 44 based on the signal from the amplifier circuit 52.The actuator 1 can offer a desired rotational property with thiscontroller.

The above-described actuator 1 can be manufactured for example in thefollowing way. FIG. 7 and FIG. 8 are longitudinal sectional views fordescribing a method of manufacturing the actuator according to the firstembodiment. For the sake of description, “upper” and “lower” in the pageof FIG. 7 and FIG. 8 is called “upper” and “lower” in the followingdescription. A step for obtaining the base member 2 is referred as StepA1, a step for obtaining the supporting substrate 3 is referred as StepA2, and a step for obtaining the actuator 1 by building up the basemember 2 and the supporting substrate 3 is referred as Step A3.

Step A1

Referring to FIG. 7A, a silicon substrate 60 is for example provided. Itis preferable that the spring constant be roughly adjusted in advance byadjusting the thickness of the silicon substrate 60 by for exampleetching. In this way, the actuator 1 having the spring constantaccommodated to an application can be easily fabricated.

Referring now to FIG. 7B, the amplifier circuit (the semiconductorcircuit) 52 is formed on an upper face of the silicon substrate 60 andat the position where corresponds to the supporting part 24. Theamplifier circuit 52 can be formed by for example diffusing an impuritysuch as boron, iridium, potassium or the like.

The stress detection element 51 (unshown in the drawing) is furtherformed at the position corresponding to the elastic part 22. The stressdetection element 51 can be formed by for example forming a metal maskwhich corresponds to the stress detection element 51 on the siliconsubstrate 60 and then diffusing an impurity such as boron or the like.

Referring now to FIG. 7C, a resin layer 70 is formed by applying a resinmaterial such as liquid polyimide on the whole upper face (the face onwhich the amplifier circuit 52 is formed) of the silicon substrate 60 byspin-coating, and then drying and fixing the material. Here a fineadjustment of the spring constants of the elastic parts 22, 23 ispossible by adjusting the thickness and/or density of the resin layer 70or selecting a type of the resin material.

Subsequently the through holes 53 (unshown in the drawing) for wiringthe amplifier circuit 52 and the stress detection element 51 are formed.

An unshown metal film of Cu, Al or the like is then formed on the upperface of the resin layer 70. At this point, the through holes 53 arefilled with the metal material forming the metal film. The metal film issubsequently etched such that the pattern of the metal film correspondsto the pattern (in plan view) of the wirings that couple the coil 43,the amplifier circuit 52 and the stress detection element 51. Throughthe above-described process, a composite substrate in which the coil 43and the like is formed on the upper face of the resin layer 70 isobtained as shown in FIG. 7D.

As a method for forming the metal film, there are a vacuum evaporationmethod, a sputtering (a low-temperature sputtering) method, a dryplating method such as an ion plating, a wet plating method such as anelectrolytic plating and an electroless plating, a thermal sprayingmethod, a bonding method of a metal sheet material and the like. Thesame method can be applied to the formation of metal films in thefollowing steps.

Referring now to FIG. 7E, a metal mask 80 that is made of for examplealuminum and that corresponds to the shapes (viewed in plan) of theweight part 21, the supporting parts 24, 25 and the elastic parts 22, 23is formed on the upper face (the face on which the coil 43 is formed) ofthe resin part 70.

The silicon substrate 60 and the resin part 70 are etched by using themetal mask 80, and the metal mask 80 is removed after the etching.Through the above-described process, a layered structure of the siliconsubstrate 60 and the resin part 70 which is etched to have the shapescorresponding to the weight part 21, the supporting parts 24, 25 and theelastic parts 22, 23 is obtained.

As an etching method, physical etching methods such as a plasma etchingmethod, a reactive ion etching method, a beam etching method, and aphoto-assisted etching method and the like are applicable here.

A metal film is then formed on the lower face of the silicon part 211 soas to form the light reflecting part 213, and the base member 2 in whichthe weight part 21, the supporting parts 24, 25 and the elastic parts22, 23 are formed to have the single body is obtained.

Step A2

Referring now to FIG. 8G, for example a silicon substrate 61 is providedas the substrate for fabricating the supporting substrate 3.

Referring to FIG. 8H, a metal mask 82 that is made of for examplealuminum and that corresponds to the area other than where the opening31 is going to be formed is formed on one face (the lower face) of thesilicon substrate 61. A metal mask 83 that is made of for examplealuminum and that corresponds to the concave portion 30 is formed on theother face (the upper face) of the silicon substrate 61.

Subsequently the silicon substrate 61 is etched through the metal mask83 till it reaches the depth corresponding to the concave portion 30.The metal mask 83 is removed after the etching. The silicon substrate 61is then etched through the metal mask 82 such that the substrate ispenetrated. The metal mask 82 is removed after the etching. Through theabove-described process, the supporting substrate 3 in which the concaveportion 30 and the opening 31 are formed is obtained as shown in FIG.8I.

Step A3

Referring to FIG. 8J, the substrate 2 obtained through theabove-described Step A1 and the supporting substrate 3 obtained throughthe above-described Step A2 are jointed through adhesive or the like soas to form the actuator 1.

The actuator 1 according to the first embodiment can be fabricated inthe above-described way.

Second Embodiment

An actuator according to a second embodiment of the invention is nowdescribed.

FIG. 9 is a perspective view of the actuator according to the secondembodiment and FIG. 10 is an explanatory drawing for a behaviordetector.

Different structures in an actuator 1A of the second embodiment from thecorresponding structures of the actuator 1 according to the firstembodiment are mainly hereunder described and descriptions for the samestructures will be omitted.

The actuator 1A according to the second embodiment has substantially thesame structure as the actuator 1 according to the first embodimentexcept for the configuration of a behavior detector 5A.

The behavior detector 5A includes a photodiode 54A (an optical element)which is provided in the weight part 21, an amplifier circuit 52A (asemiconductor circuit) formed on the silicon part 241 of the supportingpart 24, and a light source 55A provided on the supporting part 25. Thebehavior detector 5A is configured so as to detect the behavior of theweight member 21 based on a signal from the amplifier circuit 52A. Thelight source 55A is placed so as to emit a light beam from thesupporting part 25 toward the weight member 21 in the direction parallelto the X-rotational central axis.

The photodiode 54A is placed on the weight part 21 such that it canreceive the largest amount of the light beam emitted from the lightsource 55A when the weight part 21 rotates.

The amount of the light beam which the photodiode 54A receives when theweight part 21 rotates can be varied by placing the light source 55A andthe photodiode 54A in this way. The photodiode 54A has a property thatthe amount of running current or generated voltage in the photodiode 54Achanges according to the amount of light received. Therefore a value ofthe current running through the photodiode 54A and a value of thevoltage (electric signal) of the photodiode 54A varies according to therotating motion of the weight part 21. The variation in the electricsignal is then amplified by the amplifier circuit 52A. The behavior ofthe weight member 21 is detected based on the amplified signal. In thisway, the behavior of the weight member 21 can be precisely detected bythe behavior detector 5.

In this embodiment, the amplifier circuit 52A is formed on the siliconpart 241 of the supporting part 24 so that the distance between theamplifier circuit 52A and the photodiode 54A is very small. Thereby thelength of the wiring that couples the amplifier circuit 52 and thephotodiode 54A can be made short. This prevents noise from beinggenerated between the amplifier circuit 52 and the photodiode 54Athereby the behavior of the weight member 21 can be more preciselydetected.

The second embodiment of the actuator has been described. The positionwhere the light source 55A is placed is not particularly limitedprovided that the photodiode 54A can receive the light beam emitted fromthe light source 55A. For example, the light source 55A can be placed onthe supporting substrate 3 or even outside the actuator 1.

The actuator according to the invention has the light reflecting part sothat it can be applied to optical devices such as an optical scanner, anoptical switch, and an optical attenuator.

An optical scanner according to an embodiment of the invention has thesame structure as the actuator of the above-described embodiments. Morespecifically, the optical scanner includes the weight part having thelight reflecting part, the supporting parts supporting the weight part,the connecting part coupling the weight part rotatable with respect tothe supporting part and having the elastic part which is elasticallydeformable, the driving member for rotating the weight part, and thesemiconductor circuit for the driving of the weight part and/or for thedetection of the behavior of the weight part. In such optical scanner,the driving member is operated to torsionally deform and rotate theweight part. The scanner scans the light beam reflected by the lightreflecting part. The elastic part includes the silicon part mainly madeof silicon, and the resin part mainly made of resin and coupled to thesilicon part. The supporting part has the silicon part made mainly ofsilicon and coupled to the silicon part of the elastic part. Thesemiconductor circuit is provided at the silicon part of the supportingpart. In this way, it is possible to provide the optical scanner inwhich a fine adjustment of the spring constant is possible and whosesize can be minimized.

Such optical scanner can be applied to image-forming devices such as aprojector, a laser printer, a display for imaging, a bar-code reader anda confocal scanning microscope. Thereby it is possible to provide theimage forming device which has a fine image drawing characteristic.

As an example of the image forming device, a projector 9 is nowdescribed with reference to FIG. 11. For the sake of description, thelongitudinal direction of a screen S is referred as a “lateral direction(horizontal direction)” and the direction perpendicular to thelongitudinal direction of the screen S is referred as a “uprightdirection (vertical direction)” in the following description.

The projector 9 has a light source device 91 that emits light such asleaser, a cross-dichroic prism 92, a pair of light scanners 93, 94, anda fixed mirror 95.

The light source device 91 includes a red light source device 911 thatemits a red light beam, a blue light source device 912 that emits a bluelight beam, and a green light source device 913 that emits a green lightbeam.

The cross-dichroic prism 92 has four rectangular prisms which adheredtogether and the cross-dichroic prism 92 it the optical element thatsynthesizes the light beams emitted from the red light source device911, the blue light source device 912 and the green light source device913.

In the projector 9, the light beams emitted from the red light sourcedevice 911, the blue light source device 912 and the green light sourcedevice 913 based on an image information from an unshown host-computerare synthesized through the cross-dichroic prism 92. The synthesizedlight beam is scanned by the optical scanners 93, 94, and then reflectedby the fixed mirror 95, forming a color image on the screen S.

Light scanning by the optical scanners 93, 94 is now described. Thelight beam synthesized at the cross-dichroic prism 92 is scanned in thelateral direction (hereinafter called “main scanning”) by the opticalscanner 93. The scanned light beam is then scanned in the uprightdirection (hereinafter called “vertical scanning”) by the opticalscanner 94. Though the scanning, a two-dimensional color image can beformed on the screen S.

Where the optical scanner according to the embodiment of the inventionis adopted as the above-mentioned optical scanners 93, 94, it ispossible to provide the projector 9 (image-forming device) which issmall and has a fine image forming characteristic.

The rotational motion speed of the optical scanner 94 which performs thevertical scanning is generally slower than the rotational motion speedof the optical scanner 93 performs the main scanning. Though it dependson a type or size of an image, the rotation frequency of the opticalscanner 94 which performs the vertical scanning is typically about 60 Hzand the rotation frequency of the optical scanner 93 performs the mainscanning is typically about 10-256 kHz. In this extent, by adopting theoptical scanner according to the invention as such optical scanners 93,94, it is possible to easily offer the optical scanner havingappropriate torsional spring constants appropriate for the main scanningand the vertical scanning respectively. Therefore, it is possible toprovide the projector 9 (image-forming device) which is small and has afine image forming characteristic. Configuration or structure of theprojector 9 is not particularly limited provided that it can form acolored image on the screen S.

The invention is obviously not limited to the specific embodimentsdescribed herein, but also encompasses any variations that may beconsidered by any person skilled in the art, within the general scope ofthe invention. For example the structures of the actuator 1 of theinvention can be replaced by other structures that serve the equivalentfunctions. Furthermore, any structure can be added to the embodiments.

Though the structure having the symmetric shape with respect to the facewhich includes the center of the actuator and which is perpendicular tothe X-rotational central axis of the weight part and the driving member,the structure can be asymmetric.

The resin part of the weight part, the resin part of the elastic partand the resin part of the supporting part were formed so as to form asingle body in the above-described embodiment. However, the structure isnot limited to this provided that it can be strong enough for therotational motion of the weight part 21.

The elastic part has the layered structure of the resin part and thesilicon part throughout the longitudinal direction in theabove-described embodiment. The elastic part is not limited to this butcan be any structure provided that the torsional spring constants of thepair of the elastic parts are adjustable. For example, it can be anelastic part in which the silicon part and/or the resin part arepartially formed in the longitudinal direction.

Though each connecting part is formed from a single elastic part(elastic material), it is not limited as long as the weight part can berotated with it.

The number, location and shape of the elastic part provided at theconnecting part are not particularly set. For example, I: A pair ofelastic parts can be provided so as to oppose each other with therotational central axis its center when it is viewed in plan. In thiscase, each elastic part may have the layered structure of the siliconpart and the resin part or any one of the elastic parts may have thelayered structure. II: The elastic part of each connecting part may beramified in its longitudinal direction. In this case, the layeredstructure is adopted from one end of the elastic part to the ramifiedpart for example, and a rest of the part from the ramified part to theother end of the elastic part may be formed only from the silicon part.III: Each connecting part may have a first elastic part that extends onthe rotational central axis and a second elastic part that is the pairof the elastic parts opposing each other with the rotational centralaxis therebetween. In this case, the first elastic part may be made onlyfrom the silicon part and the second elastic part may be made from thelayered structure of the silicon part and the resin part.

Though the above-embodiments are the single-degree-of-freedom vibrationsystem, it is not limited. For example a second-degree-of-freedomvibration system can be adopted as long as the weight part can berotated. More specifically, each connecting part may have a plate-shapeddriving member, a first elastic part that coupled the driving member andthe supporting part, and a second elastic part that couples the drivingmember and the weight part. In this case, the layered structure of thesilicon part and the resin part is formed at least in a part of thefirst elastic part and/or the second elastic part.

1. An actuator, comprising: a weight part; a supporting part supportingthe weight part; a connecting part coupling the weight part rotatable tothe supporting part and having an elastic part; a driving member drivingand rotating the weight part, wherein the driving member includes a coilprovided on the weight part and a voltage supply applying a voltage tothe coil, the weight part is rotated by applying the voltage to the coilthrough the voltage supply; an amplifier circuit driving the weightpart; and a behavior detector detecting the behavior of the weight partbased on a signal received from the amplifier circuit, wherein thedriving member is operated to torsionally deform the elastic part androtate the weight part, the elastic part includes a resin layer and thetorsional spring constant of the elastic part is adjusted by thethickness of the resin layer, the supporting part includes at least asecond layer, the amplifier circuit being disposed on the second layer.2. The actuator according to claim 1, wherein the behavior detectorincludes a stress detection element detecting a stress of the elasticpart.
 3. The actuator according to claim 1, wherein the behaviordetector includes a light source and a photodiode receiving a light ofthe light source.
 4. An optical scanner, comprising: a weight parthaving a light reflecting part that has a light reflecting property; asupporting part supporting the weight part; a connecting part couplingthe weight part rotatable to the supporting part and having an elasticpart; a driving member driving and rotating the weight part, wherein thedriving member includes a coil provided on the weight part and a voltagesupply applying a voltage to the coil, the weight part is rotated byapplying the voltage to the coil through the voltage supply; anamplifier circuit driving the weight part; and a behavior detectordetecting the behavior of the weight part based on a signal receivedfrom the amplifier circuit, wherein the driving member is operated totorsionally deform the elastic part and rotate the weight part, theelastic part includes a resin layer and the torsional spring constant ofthe elastic part is adjusted by the thickness of the resin layer, thesupporting part includes at least a second layer, the amplifier circuitbeing disposed on the second layer.